Marin County continues to be infested with Sudden Oak Death, the disease caused by the pathogen Phytophthora ramorum. Increased infestations have been detected in West Marin. Tree mortality in wild land and urban/wild land interface areas causes dramatic changes in the landscape, affecting ecosystems, increasing fire and safety hazards, and decreasing property values.

P. ramorum hosts include native woodland trees and understory plants, as well as ornamental nursery plants. Currently there are over 100 native and ornamental hosts; new hosts continue to be found and added to the state and federal quarantines.

On oaks, P. ramorum causes potentially lethal trunk cankers; on other hosts it causes a rarely lethal leaf or twig blight. Tanoaks may have both trunk cankers and leaf dieback. Unlike oaks, some hosts (i.e. California Bay Laurel) are not killed by this pathogen; instead these hosts are a vector, allowing inoculum to spread through natural or artificial means (rainwater, soil, infested nursery stock) under moist conditions.

The phosphonate product Agri-Fos® continues to be the only registered product for control of SOD on oaks. It works best as a preventative, stimulating the tree's natural defense system to fight the disease.

The California Oak Mortality Task Force (COMTF) was established in 2000 to research and understand SOD. More information, including diagnostic guides and management recommendations may be found at http://www.suddenoakdeath.org/